1. Field of the Invention
The present invention relates to a technology for adjusting the quality of a displayed image.
2. Discussion of the Background
Sharpness adjustment is one of well-known methods of image processing. In some image display apparatuses such as projectors, the sharpness adjustment can be setup by users. When performing the sharpness adjustment, image quality can be improved by enhancing sharpness of a diffused image, or by removing high frequency noises at the more or less sacrifice of sharpness (acutance).
Various filters with different frequency characteristics are used in the sharpness adjustment, such as a smoothing filter or a differential filter. For example, a smoothing filter is used to remove high frequency noises contained in an image, and a differential filter is used to punctuate edges of an image by amplifying high frequency components.
However, in typical sharpness adjustment, not only is the sharpness of an image adjusted, but contrast and brightness of an image are also affected. Accordingly, there arises a problem that when the set value of sharpness adjustment is changed by a user, contrast and brightness of an image will then be varied also. This problem is not limited to a case of performing sharpness adjustment, and is a common problem found in adjustments of various image qualities other than contrast and brightness.